Wasp and Scale Insects Help Control Giant Reed

Agricultural Research Service (ARS) scientists released the arundo gall wasp and the arundo scale several years ago as part of a biocontrol program to kill giant reed along Texas’ Rio Grande. The weed, also known as “carrizo cane” and “Spanish reed,” clogs streams and irrigation channels, weakens river banks, stifles native vegetation, affects flood control, reduces wildlife habitat, and impedes law enforcement activities along the international border.

Recent research conducted by entomologist John Goolsby, with the ARS Tick and Biting Fly Research Unit in Edinburg, Texas, demonstrates that these insects have helped control giant reed over more than 550 river miles. Measurements taken in 2014 documented a 22-percent decrease in plant biomass along the Rio Grande since the insects’ release in 2009. Measurements in 2016 show a further decrease of 28 percent and significant recovery of native riparian vegetation.

Giant reed grows between three and seven inches a day and reaches heights of 30 feet along the Rio Grande, according to Goolsby. The weed worsens cattle fever tick invasion by creating an ideal habitat, making it difficult for USDA inspectors to detect tick-infested cattle and deer. As the riverbank transitions back to native vegetation, this plant community supports greater abundance and diversity of tick-feeding ants and beetles that act as a biological control.

ARS is partnering with universities, other U.S. agencies, and Mexican government officials in an effort to manage giant reed.

To accelerate weed removal, scientists have combined “topping”—mechanically cutting cane—with insect releases. Topping suppresses growth for more than a year and makes plants more susceptible to insect attacks. Combining topping and insect releases gives a high, long-term suppression of cane and allows native trees to grow and start shading giant reed, according to Goolsby.

Read more about this research in the October 2016 issue of AgResearch online.